In my opinion, the first step is understanding the vernacular more so than where to look. I think this is generally a good post but, a couple of subjects warrant comment (opinion...which yes, I know how valuable anyone's opinion may or may not be).
* In my world (Bank) a "Foreclosure" is a property/loan that has a filed notice (Often referred to as first legal) that a foreclosure has commenced and is somewhere in the foreclosure process between first legal and sale (or post sale redemption).
*In my world, a "Pre-foreclosure" is a property or loan where the first legal has not been filed. It is delinquent enough (Greater than 90 days but below 120 days(can't file first legal until after the 120th day by federal rule (Except under very very specific circumstances)) to where the lender or servicer has sent the breach letter (Notice of pending foreclosure) with an expiration date that the loan will be referred to a foreclosure filing (Trustee/attorney) if the borrower(s) don't cure the breach within that defined period of time.
* A notice of default is not a letter sent by a creditor saying they are late. It is actually the legal filing that there is a recorded foreclosure process that has already started, after the expiration of the letter that was sent informing of the lates and consequences of no action.
* lis pendens is not just a note but a recorded cloud on title that there is pending litigation. Lis pendens are not typical in trustee states because trustee states use the power of sale clause to foreclose, and don't use the courts.
*Online Directories are only available for or useful for loans/borrowers in an active foreclosure where there has been a public filing in court or the recorder's office. Delinquent loans under 120 days, are not public information for anyone.
*Asset Managers manage foreclosed (past tense), not foreclosure (Pending sale/auction) properties. Those are called "REO"(Real Estate Owned) (as you pointed out), not foreclosures.
*Short sales don't exist today. 2016? Sure. 2024? Maybe in Jersey but nowhere else (I'm being somewhat sarcastic about Jersey). Short sales are where the bank would realize a lesser loss settling than they would completing a foreclosure. It's usually a financial distress but not always. For example, a soldier changing duty station could do a short sale without any hardship whatsoever. Short sales by design are listed on MLS (always and always are arms length) and not below value, or the lender would more than likely decline any short sale offer.
*Banks don't list foreclosure listings on their websites. REO properties? You bet, but not active or pre-foreclosure.
*Real Estate attorneys are a waste of time if you are looking for foreclosures. Using one to go under contract is fine but using (networking) one to find a foreclosure? Highly unlikely except in a probate or estate type of scenario.
*Auction Houses are good for finding active foreclosures and REOs (Bank owned). If you agree with my definition (I'm not insisting you do) of "pre foreclosure", you wouldn't find pre-foreclosures at an auction house.
*Neighborhood drive bys could get you shot. Drive slow up/down the wrong street looking like you aren't from there could get the cops called on your or worse. You won't see a notice for a preforeclosure. Any required notice would be removed quickly (usually) if occupied.
I highly recommend against this tactic as you are going to swing a bat at a hornets nest or worse, knocking on their door. You may also run afoul of local/state laws against people that contact people in foreclosure to buy their home.
*Wholesalers are often people that don't have the financial wherewithal to do the deal themselves, so they try to get others to help and call themselves wholesalers. Yes, I know there are legitimate wholesalers but just like used car salesmen (women), the bad ones make the good ones seem just as bad. They don't usually stop foreclosures and usually blow things up instead.